FIG. 1 shows an anesthesia machine that can control the anesthetic inhalation and mechanical ventilation for a patient during surgery. The gas inhaled by the patient can be circulated in a closed-loop breathing circuit equipped with a carbon dioxide absorber. The carbon dioxide absorber may contain dry soda lime for absorbing the carbon dioxide exhaled by the patient. Due to oxygen consumption by the patient and undesirable leakage, the gas circulated in the breathing circuit may decrease gradually. Thus the anesthesia machine often employs an independent channel for constantly supplementing gas into the breathing circuit. The gas supplemented through this independent channel can be called fresh gas.
The fresh gas may be formed in two steps: different flows of oxygen and equilibrium gas (such as air or nitrous oxide) may first be mixed in a flow monitor; the mixed gas outputted from the flow monitor may then be passed through an anesthetic volatilization device (containing some anesthetic) to form the fresh gas to be delivered into the breathing circuit.
The flow monitor may mechanically and/or electronically regulate flows of the oxygen and the equilibrium gas.
For the mechanical regulation, a mechanical needle valve can be used by a user for such flow regulation, and a flow sensor or a mechanical rotameter can further be used for monitoring the flows of the oxygen and the equilibrium gas. This mechanical regulation mode can be implemented with simple systems with low cost and high reliability, while it may not be adequate in terms of automation. In addition, the user may need to manually calculate the desired flows of the oxygen and the equilibrium gas so as to obtain desired oxygen concentration and total flow. Consequently, the mechanical mode is generally employed in low and medium-grade anesthesia machines.
For the electronic regulation, a user may need to input desired oxygen concentration and total flow, and then the regulation system can monitor respective gas flows to meet a regulation target set by the user. This electronic regulation mode thus can have high automation, simple operation and high accuracy, but the systems used may be complicated with high cost. As a result, the electronic mode is generally employed in middle and high-grade anesthesia machines.
Flow monitors using electronic regulation mode are often called as electronic flow monitors.
FIG. 2 shows an existing electronic flow monitor, which can include an oxygen branch 2, an oxygen bypass 1, a nitrous oxide branch 3 and an air branch 4.
The oxygen branch 2 may be arranged with an on-off controller 7 (e.g., gate valve), a flow control valve 8, a pressure sensor 10, a flow sensor 9 and a one-way valve 11.
The nitrous oxide branch 3 and the air branch 4 may be respectively equipped with an on-off controller 7, where at most one of these two on-off controllers can be in an “on” state at any given instant. A shared gas branch 5 can also be arranged for the nitrous oxide branch 3 and the air branch 4, and the shared gas branch 5 can be equipped with a flow control valve 8, a pressure sensor 10, a flow sensor 9 and a one-way valve 11.
A gas mixing branch 6 may include a pressure sensor 10. The oxygen bypass 1 may be equipped with a mechanical needle valve 12 and an on-off controller 7. This on-off controller 7 is in an “on” state (i.e., open) when there is no power supply. This is different from the rest of the on-off controllers used in the electronic flow monitor, which would be in an “off” state (i.e., closed) when there is no power supply. In this way, the oxygen bypass 1 can be switched to an “on/open” state to supply pure oxygen to the patient in case the power is lost. The mechanical needle valve 12 can be used for regulating gas flow, and the on-off controller 7 can prevent any oxygen from flowing through the oxygen bypass 1 during normal operation when the mechanical needle valve 12 is not closed completely.
The pressure sensors 10 in the oxygen branch 2, the shared gas branch 5 and the gas mixing branch 6 may perform pressure measurement on the gas circuits so as to avoid high pressure therein and improve system security. Moreover, the gas flow can be compensated according to the information obtained from the pressure sensors 10.
The one-way valves 11 in the oxygen branch 2 and the shared gas branch 5 may prevent backflow of the gas in the oxygen branch 5 and an equilibrium gas branch (i.e. the air branch and the nitrous oxide branch).
The above-described electronic flow monitor may have the following disadvantages: in addition to some flow control valves for the flow regulation, the on-off controllers 7 are also used in the oxygen branch 2, the air branch 4 and the nitrous oxide branch 3 for on-off control of the corresponding gas circuits. Those on-off controllers 7 may lead to high cost and complicated structure.